DESCRIPTION (Adapted from the applicant's description): The continuing spread of HIV and other STDs has produced a large and growing volume of research directed at examining the demographic, behavioral, and attitudinal factors that are associated with the use or nonuse of condoms for disease prevention. However, the majority of this research holds that the choice faced by couples is whether to sacrifice the greater pregnancy protection offered by alternative methods for the STD protection provided by condoms. The fact that some women choose to use a highly effective method together with condoms has been largely ignored by researchers, even though the dual use of these methods maximizes a woman's level of protection from both threats. Thus, the determinants and consequences of this choice are not well understood. The proposed study will address this gap in our knowledge by using data from the newly released Cycle V of the National Survey of Family Growth to develop a detailed, dynamic model of women's method and relationship behaviors. This model will be based on a system of hazard models of transitions between specific states defined on the basis of both method type and relationship status. The estimates obtained from these hazard models will be used to implement simulation models that will allow the investigator to capture and describe the experiences of women as they move among the multiple states defined in the study. By adopting this approach, the proposed study will maintain the woman as the central focus of the analysis while allowing an examination of the impact on dual use of the relationship context within which method use decisions are made. In this way, the results of the proposed study may provide a comprehensive understanding of the role of both individual and relationship factors in determining women's dual use experiences. It may also yield policy-relevant information that may be used to promote this method option.